The colour of Alpha Centauri

Last night I noticed that Alpha Centauri seems more orange than usual
compared to Beta Centauri.

Has someone else also noticed this?

Any explanations?

Jack:
Last night I noticed that Alpha Centauri seems more orange than usual
compared to Beta Centauri.

Has someone else also noticed this?

It would be difficult for me to explain without knowing the star's
elevation at the time of the observation, weather conditions, and air
quality.

I can recall when I was a child looking at Sirius through binoculars
from a point some miles south of Pittsburgh, and Sirius was often as
red as blood when it was down in the muck. Since Pgh. was at that time
"the steel capital of the world" there was usually plenty of muck in
the sky.

In the Pittsburgh steel-making suburb of Donora, just a few miles from
my hometown, at least 68 people died between October 26 and October 31,
1948, because they made the mistake of walking outside their houses and
breathing. Hundreds of others suffered permanent heart and/or lung
damage. See "When Smoke Ran Like Water" by Devra Davis

Davoud

--
usenet *at* davidillig dawt com

On Apr 7, 2:43 pm, Davoud wrote:

It would be difficult for me to explain without knowing the star's
elevation at the time of the observation, weather conditions, and air
quality.

I observerd Alpha Centauri last night just after ten pm local time. (8
pm UT).

The star from my location in Pretoria, South Africa (25° 24' S, 28°
12' E) had an altitude of 38°

The sky was clear - ahead of a cold front. Beta had a bright white
color as usual but Alpha's seemed more like that of Mars.

Davoud:
It would be difficult for me to explain without knowing the star's
elevation at the time of the observation, weather conditions, and air
quality.

Jack:
I observerd Alpha Centauri last night just after ten pm local time. (8
pm UT).

The star from my location in Pretoria, South Africa (25° 24' S, 28°
12' E) had an altitude of 38°

The sky was clear - ahead of a cold front. Beta had a bright white
color as usual

That kills my rose-colored glasses theory.

but Alpha's seemed more like that of Mars.

Davoud

--
usenet *at* davidillig dawt com

On Apr 7, 1:51*am, Jack wrote:
Last night I noticed that Alpha Centauri seems more orange than usual
compared to Beta Centauri. snip Any explanations?

I'm too far north to provide any confirmation by observation.

As to possible explanations based on variable star types verses
atmospheric effects, alf Cen (Rigil Kentaurus) is a double of G (v
-0.0, alf Cen A) and K (v 1.33 , alf Cen B) class. The AAVSO VSX
database lists alf Cen A as a suspected variable star of the BY
Draconis-type under the designation NSV 20145 with a magnitude range
between -0.3 to -0.0.

http://www.aavso.org/vsx/ Search on "NSV 20145"

BY Draconis-type stars are rotating variables whose apparent
luminosity changes primary as a result of cooler or brighter parts of
the star being pointed towards Earth as a result of the star's
rotation. http://www.sai.msu.su/groups/cluster...ii/vartype.txt

I was not able to find a period or light-curve for alf Cen A on the
AAVSO site. The AAVSO site links to an All-sky Automated Survey
(ASAS-3) light-curve for alf Cen A, but frankly, I am having trouble
interpreting the plot. "NSV" stands for the "New Catalogue of
Suspected Variable Stars" and is a compliation of about 15,000 suspect
variables made during the 1980s.

Another possibility to consider is that alf Cen A-B has not changed in
brightness, but that bet Cen (Hadar) is relatively brighter. bet Cen
(Hadar) is a B class star. bet Cen is listed in the AAVSO VSX
database as a known variable of the beta Cephid-type with a magnitude
of range of 0.6 to 0.0 and a period of 0.157 days.

Hope that helps. - Canopus56

On Apr 8, 2:55 am, canopus56 wrote:

As to possible explanations based on variable star types verses
atmospheric effects, alf Cen (Rigil Kentaurus) is a double of G (v
-0.0, alf Cen A) and K (v 1.33 , alf Cen B) class. The AAVSO VSX
database lists alf Cen A as a suspected variable star of the BY
Draconis-type under the designation NSV 20145 with a magnitude range
between -0.3 to -0.0.

Thank you for the information.

I had another look last night with an 8x40 binocular and compared
Alpha to Gacrux (the head star of the cross).

Alpha is definitely not as red as Gacrux but more so than Beta.

The difference in magnitude is also more pronounced than what I can
remember (mag 0.14 for a Centauri vs mag 0.58 for b Centauri).

The variability of Beta is probably the culprit!

Jack wrote in news:842bac25-0530-4b55-a989-
:
snip
The variability of Beta is probably the culprit!

I am out of practice on visual magnitude comparsions. Unless you do it
consistently, it is hard to judge below 0.5 mag intervals visually. That
you noticed a variation at all shows a sharp eye. It's an enjoyable way to
spend some time with binoculars. - Canopus56
** Posted from http://www.teranews.com **